The present invention relates to a rotary head apparatus and more particularly to a rotary head apparatus, e.g., a cylinder motor for video tape recorders (hereinafter simply referred to as VTRs) which is well suited for recording on and reproducing magnetic signals from a recording medium.
The prior art rotary head apparatus have been generally so designed that the construction of its builtin motor includes a magnetic yoke integral with a coil within its stator as disclosed in Japanese Patent Publication No. 39-16166 and JP-A-59-60729. However, this conventional construction is disadvantageous in that during rotation of the rotor magnet, an attraction is caused between the rotor magnet and the yoke within the stator and this tends to cause a cogging torque, increase the wear of the bearings and damage the bearings. Another disadvantage is that due to the occurrence of a magnetic field variation in the yoke assembled integrally with the coil, an iron loss is caused and the motor efficiency is deteriorated. Still another disadvantage is that the magnetic field distribution in the magnetic gap tends to be disturbed and is low in uniformity. This magnetic field distribution intersects the stator coil thus tending to increase the variation of the generated torque. To overcome these disadvantages, it is essential to form a magnet magnetic circuit by decreasing the number of magnetic materials within the stator as far as possible.